The design of trucks for railway locomotives involves consideration of many factors such as load carrying capacity, dynamic stability, rail loading and weight distribution, tractive power capacity, adhesion efficiency and friction and wear of wheels and rails. For larger locomotives, trucks having multiple powered axles are generally required to provide the desired load supporting and tractive effort capabilities. Numerous forms of such trucks have been used or proposed including two, three and four axle arrangements having axles connected with a single frame as well as multiple frame truck units connected by a span member, each arrangement providing its own particular set of operating characteristics.